containing radioactive material on its way from a hospital in tijuana to a disposal site near mexico city. tonight the truck has been found near the gas station where it was stolen. and the critical cargo known as cobalt 60 has been recovered. mexican officials describe its radioactivity now as quote, low intensity. >>> the commuter train derailment in new york city this weekend has thrust the topic of worker fatigue into the news. the investigation, as you may know, is now focused on the engineer and whether he fell asleep two weeks into a new shift in a 5:00 in the morning start. everyone gets tired, every shift has its own rhythms. we get our report tonight from tom costello. >> reporter: in the first minutes of sunday's emergency response, william rockefeller told police he zoned out just before the crash. his attorney said he was in a daze situation. a union rep said he nodded out. different descriptions for what sleep researchers say sounds like a sleep attack. >> when sleep intrudes involuntarily into the waking brain and seizes control of the brain so that the person who is doing